Thyroid follicles, C cells and parathyroid !
- Organ
The thyroid stores its hormone in colloid-filled follicles; the parathyroids, stuck behind it, control blood calcium.
Updated 2026-11-01
See it in 3D: Thyroid gland · Parathyroid glands
What it is
The thyroid is built of follicles: spheres of epithelium enclosing colloid rich in thyroglobulin, where T3 and T4 are stored. Between the follicles sit the parafollicular or C cells, which make calcitonin. Behind the thyroid there are usually four parathyroids, whose chief cells secrete PTH. The height of the follicular epithelium and what surrounds the follicles let you recognise most thyroid diseases.
Structure
- Thyroid on H&E: follicles of varying size with smooth pink colloid, surrounded by rich capillaries.
- C cells: larger and paler than follicular cells, single or in groups between follicles or at the base of the follicular epithelium.
- Parathyroid: packed cords of small chief cells, large pink oxyphil cells and adipocytes between them.
Function
- Follicular cells take up iodide, make thyroglobulin and, when TSH stimulates them, resorb colloid and release T4 and T3.
- Calcitonin lowers calcium by restraining osteoclasts; its role in adults is minor.
- PTH raises calcium: it frees calcium from bone, reabsorbs it in the kidney and activates vitamin D.
Thyroid and parathyroid under the microscope in the key diseases
| Disease | What you see |
|---|---|
| Graves disease | Tall, hyperplastic follicular epithelium with papillae; scant, scalloped colloid |
| Hashimoto thyroiditis | Lymphoid infiltrate with germinal centres, atrophic follicles and Hürthle (oncocytic) cells |
| Papillary carcinoma | Papillae with clear, overlapping nuclei, grooves, pseudoinclusions and psammoma bodies |
| Medullary carcinoma | Nests of C cells with amyloid stroma; high calcitonin; may be hereditary (MEN 2) |
| Parathyroid adenoma | Nodule of chief cells with little fat, beside a rim of compressed normal gland |
Markers
- Thyroglobulin
- TTF-1
- Calcitonin
- Congo red (amyloid)
- PTH
Clinical notes
- Iodine-deficiency goitre: more TSH and follicles that grow without being able to make more hormone; still present in Latin American highland areas, though iodised salt has cut it sharply.
- Thyroid surgery: injuring or removing the parathyroids causes hypocalcemia with tingling and tetany.
- Fine-needle aspiration of a nodule is read from the architecture and nuclei of the follicular cells.
Test yourself
Think of the answer, then tap the question to see it.
What does a very active thyroid follicle look like?
Tall cuboidal or columnar epithelium with scant colloid and scalloped edges from resorption, as in Graves disease.
Which thyroid tumour arises from C cells and what does it make?
Medullary thyroid carcinoma; it makes calcitonin and usually has amyloid deposits.
Which nuclear findings suggest papillary thyroid carcinoma?
Clear ground-glass, overlapping nuclei with grooves and pseudoinclusions, often with psammoma bodies.
Which parathyroid cells secrete PTH?
The chief cells.
See it in 3D
The structures of Durgical's 3D anatomy where it is found.
Related
- Pituitary: adenohypophysis and neurohypophysis
- Glands: exocrine vs endocrine, secretion types
- Bone tissue: cells, compact and spongy bone
Related conditions
- Graves disease (hyperthyroidism)
- Hypothyroidism
- Thyroid cancer (papillary)
- Thyroid nodule
- Primary hyperparathyroidism
Educational content on normal microscopic structure and its clinical relevance; no substitute for studying slides or for a health professional's advice.
Sources: 17.4 The Thyroid Gland (OpenStax, Rice University, 2022); 17.5 The Parathyroid Glands (OpenStax, Rice University, 2022); Thyroid & Parathyroid Glands (National Cancer Institute, SEER Training Modules, 2026).
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Representative model, for educational purposes only.